Nature of a Low Molar Mass Peak in Anionic Poly(-caprolactam). Its Identification as Macrocyclic Ensemble
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- 作者：Elena Casazza ; Laura Ricco ; Saverio Russo ; Emilio Scamporrino
- 刊名：Macromolecules
- 出版年：2007
- 出版时间：February 6, 2007
- 年：2007
- 卷：40
- 期：3
- 页码：739 - 745
- 全文大小：352K
- 年卷期：v.40,no.3(February 6, 2007)
- ISSN：1520-5835
文摘
It has been found that anionic poly(
-caprolactam) exhibits the peculiarity of a secondary SECpeak at intermediate elution times between the traces pertaining to the high polymer and those of the extractedoligomer fraction, irrespective of the conditions of synthesis, either nonisothermal (quasi-adiabatic) or isothermal.As yet, such a peak has never been evidenced in the literature. Synthesis in isothermal conditions at relativelylow T allows to get rid af all structural irregularities, linked to nonisothermal anionic conditions, and analyze indepth the nature and extent of the above peak. Together with other characterization techniques, MALDI-TOFanalysis has revealed that the peak is entirely composed of macrorings made of multiples of -caprolactam repetitionunit, typically from M9 to M19, in amounts linked to the experimental conditions of the synthesis, but usually ofca. 2.5 wt %, as referred to the high polymer content. This amount is exceedly larger than the value extrapolatedfrom the lower oligomer (x 
8) content and cannot be justified by any ring-chain thermodynamic equilibriumapproach. On the other side, also for lower oligomers striking discrepancies exist between theory and experimentalresults. A general overview, including also cyclic oligomer content in hydrolytic poly(-caprolactam) samples, isprovided, and a critical analysis of the extraction methods described so far in the literature is given.
-caprolactam) exhibits the peculiarity of a secondary SECpeak at intermediate elution times between the traces pertaining to the high polymer and those of the extractedoligomer fraction, irrespective of the conditions of synthesis, either nonisothermal (quasi-adiabatic) or isothermal.As yet, such a peak has never been evidenced in the literature. Synthesis in isothermal conditions at relativelylow T allows to get rid af all structural irregularities, linked to nonisothermal anionic conditions, and analyze indepth the nature and extent of the above peak. Together with other characterization techniques, MALDI-TOFanalysis has revealed that the peak is entirely composed of macrorings made of multiples of -caprolactam repetitionunit, typically from M9 to M19, in amounts linked to the experimental conditions of the synthesis, but usually ofca. 2.5 wt %, as referred to the high polymer content. This amount is exceedly larger than the value extrapolatedfrom the lower oligomer (x 8) content and cannot be justified by any ring-chain thermodynamic equilibriumapproach. On the other side, also for lower oligomers striking discrepancies exist between theory and experimentalresults. A general overview, including also cyclic oligomer content in hydrolytic poly(-caprolactam) samples, isprovided, and a critical analysis of the extraction methods described so far in the literature is given.